The operation of an internal combustion engine such as, for example, a diesel, gasoline, or gaseous-fuel powered engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and oxides of nitrogen (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of the engine piston forces exhaust gas, which may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.
Research is currently being directed towards decreasing the amount of undesirable emissions that are exhausted to the environment during the operation of the engine. It is expected that improved engine design and improved control over engine operation may lead to a reduction in the generation of undesirable emissions. Many different approaches such as, for example, exhaust gas recirculation (EGR), water injection, and fuel injection timings, have been found to reduce the amount of emissions generated during the operation of the engine. Aftertreatment solutions such as, for example, traps and catalysts, have also been found to effectively remove emissions from an exhaust flow. However, because some of these solutions require increased exhaust temperatures, their efficient implementation sometimes requires non-typical engine valve events.
The engine valves in an internal combustion engine are typically driven by a cam arrangement that is operatively connected to a crankshaft of the engine. The rotation of the crankshaft results in a corresponding rotation of a cam that cyclically drives one or more cam followers. The movement of the cam followers results in the actuation of the engine valves, and the shape of the cam governs the timing and duration of the valve actuation. In order to produce a non-typical engine valve event, a variable valve actuation device that interrupts the cyclical movement of the valves is required.
One type of variable valve actuation device includes a hydraulic master/slave piston combination, as described in U.S. Pat. No. 6,125,585 (the '585 patent) issued to Hu on Oct. 3, 2000. Specifically, the '585 patent describes an internal combustion engine having an exhaust valve connected to a lobed cam by way of hydraulic linkage. As the lobed cam rotates, a master piston is displaced within a cylinder to pressurize fluid in the linkage. As the fluid is pressurized, a slave piston connected to the exhaust valve is displaced from an associated cylinder to reciprocatingly move the exhaust valve in accordance with cam rotation. To vary the actuating motion of the exhaust valve (i.e., lose valve lift by delaying valve opening or completely eliminate valve lift), some amount of the pressurized fluid is spilled from the linkage before pressurizing begins, thereby effectively shortening the linkage length. By selectively changing the exhaust valve's opening profile, exhaust treatment solutions such as EGR can be implemented.
Although the variable valve actuation device of the '585 patent may be effectively used to recirculate exhaust gas and, thereby, reduce an engine's emissions, it may be limited. In particular, the motion of the exhaust valve, as described in the '585 patent, is directly connected to motion of the lobed cam and, thus, the exhaust valve can only open, close, and/or have a maximum lift that corresponds with the rotational timing of the cam and the cam lobe profile. There may be situations where valve opening is desired but the cam lobe is not in a position to contact the master piston. In these situations, the device of the '585 patent would provide no assistance.
The valve actuation system and method of the present disclosure solve one or more of the problems set forth above.